I am planning a coop for 6-10 chickens and welcome suggestionns.
My own thoughts are:
Regarding exterior access for collecting eggs -- does not matter, ecause as long as the boxes are on an exterior wall, you can build an access door. You can have inside nest boxes with an access door (and you could even have exterior boxes with egg access only from inside).
I'd reommend outside access even if you expect to be going inside the coop anyway, as it makes checking for eggs so convenient. (Note: the access door only needs to be big enough to reach the eggs. A good idea, though, is to also plan a way to remove the bedding conveniently (from either outside or inside. One way is to make the board holding the bedding in (on either the interior or eterior side) removable.)
Exterior nest boxes advantages:
Saves space and simplifies the layout inside the coop. Avoids the problem of hens laying in the space underneath the boxes or dirtying the tops.
Interior nest boxes advantages:
Simpler construction and a less cluttered-looking exterior. Better temperate buffering both winter and summer. (The eggs will not freeze as fast in winter, and the boxes will not get direct hot sun in summer.) Also less of an issue with rain-proofing the boxes. For those in a snowy climate, need to keep in mind that the roof or lid over exterior boxes will collect snow.